lakes and streams around the world, arizona michigan, arkansas, the uk and france. researchers believe the goldfish are introduced by people emptying fish bowls into lakes and streams. it confirms a new threat to the ecology of lake tahoe. >> the small little things that people do can have a large impact when you consider that you know, probably not just one person doing it. >> reporter: biologists believe if the numbers grow goldfish could ultimately affect lake tahoe renounced clarity. >> at lake tahoe we're trying to keep the lake crystal clear and excreteing nutrients will promote algae growth. >> reporter: it shows how easy it is for an invasive species to take hold. new details tonight involving olympic star accused of murder. investigators explain what neighbors say they heard right before oscar pistorius'